The invention relates to a safety bumper having a bumper body consisting of an elastic foamed material and having a supporting plate and an electric switching device in the form of a strip-shaped contact arrangement which switches when outside pressure is exercised on the bumper body.
Safety bumpers of this type are known (Safety Bumper Brochure of MAYSER Polymer Electric, Imprint SB/5/2.89/D). Safety bumpers of this type are used, for example, for being mounted on robots or unmanned transport systems in order to cause an immediate stoppage of such devices should these come in contact with persons in an unintended manner. The advantage of such safety bumpers is the fact that such shut-off devices, because of the construction of the foamed-material bumper, have no sharp edges and also cannot be bent.
In the known constructions, the design is such that the switching device consists of two flexible strips. As a rule, one strip is fastened directly to a supporting plate arranged on the rear of the safety bumper while the other strip is arranged at the foamed bumper body at a corresponding distance to the first strip in a hollow space created for this purpose. Since, as a rule, the foamed bodies are covered toward the front with an airtight and watertight skin, it is necessary to leave the supporting plates open toward the rear so that the foamed material which is used as the elastic element for the approaching and moving away of the switching strip can be compressed in the desired manner while discharging part of its air volume and, mainly because of the returning air, can resume its initial position which had existed before a deformation. Safety bumpers of this type can therefore be used only to a limited extent at locations with high air pollution or high humidity because the relatively sensitive switching strips are affected in an undesirable manner. In addition, the fastening of one of the switching strips to the foamed body requires a relatively expensive manufacturing.
It is an object of the invention to develop a safety bumper of the initially mentioned type in such a manner that the device becomes less sensitive to outside influences and its manufacturing is facilitated.
For achieving this object, it is provided in the case of a safety bumper of the initially mentioned type that the supporting plate is equipped with a frame and in that the contact arrangement is constructed as a switching strip fastened to the supporting plate inside the hollow space formed by the frame, an elastically bendable pressure strip, which is arranged on the opposite wall of the hollow space and is provided particularly with elevations for the contacting of the switching strip, being assigned to the switching strip. By means of this design, the foamed material takes over only a shock absorber function and, at points at which it is pressed from the outside, exercises a force on the pressure strip which will elastically bend at this point. It touches the switching strip, which is completely sealed in itself, for the purpose of making contact. The elastic pressure strip restores itself automatically. In the case of the design according to the invention, the elastic pressure strip forms the elastic restoring element which, in the known arrangements was formed by the foamed material. By means of the new development, the making of contact cannot be disadvantageously affected by environmental influences (dusty or humid air) because the contact takes place inside the switching strip which is sealed off. Nevertheless, a sensitive triggering is maintained. The elastic pressure strip, in each case, provides the required switching pressure. In this case, it is advantageous that the switching strip is arranged inside a hollow space which is surrounded by firm walls and which is fixedly connected with the supporting plate carrying the switching strip. This permits an extensive pre-assembling and creates a robust construction.
According to certain preferred embodiments, it is advantageous to provide the pressure strip with elevations for the contacting of the switching strip because the local pressure forces exercised on the switching plate can be increased in this manner and the reliability of the triggering of a switching operation becomes higher. Each bending of the pressure strip therefore, if the distances of the webs are selected correspondingly, will result in some sort of point contact of the pressure strip which reliably triggers the desired switching operation.
A particularly advantageous embodiment of the invention includes an arrangement wherein the frame is provided with an inwardly directed edge extending at least on the opposite longitudinal sides and wherein the pressure strip rests against the inner edge of this edge. In this case, the frame is simultaneously also used as a holding device for the pressure strip so that the complete switching device, comprising the switching strip, the supporting plate, the frame and the pressure strip, may be premounted without the foamed body. Despite the resting of the pressure strip against the lower edge of the edge of the frame, a flush contact with the foamed body takes place according to preferred embodiments wherein the pressure strip is provided with an elevation projecting into the area between the inner edges of the edge which face one another, and wherein the elevation has a height corresponding to the thickness of the edge. In certain preferred embodiments, the bumper body can be glued directly on the edge facing away from the switching strip.
Certain preferred embodiments include an arrangement wherein the frame and the supporting plate are parts of a one-piece profiled strip having a C-shaped cross-section, and wherein the open faces of the profiled strip are closed off by inserted closing pieces. This arrangement permits a particularly simple and economical manufacturing because it is sufficient to cut the length of the profiled strip from an extruded profile which may, for example, be made of aluminum or plastic. The safety bumper, having a specific length, will then be produced in a simple manner by inserting closing caps on the face side, and the foamed body may then be glued on, in which case, this foamed body must be provided only with a smooth underside and not, as in the state of the art, with a hollow space. The new design therefore permits an economical series production which can also be automated.
Certain preferred embodiments include an arrangement wherein the bumper body is covered by an impermeable skin which is tightly connected with the surrounding frame or the lateral walls of the profiled strip, and wherein a lattice-type fabric band is provided under the skin in the area of the lateral walls of the bumper body and the outer walls of the profiled strip, the fabric band being used for the fastening of the bumper body to the profiled strip, on the one hand, and, on the other hand, for the fastening of the skin to the bumper body and to the profiled strip. These features finally offer special advantages with respect to the fastening of the foamed bumper body on the pre-assembled switching device.
The invention is illustrated in the drawing by means of embodiments and will be described in the following.